Steam News has word that the PC edition of The Passing DLC is now automatically available for free via Steam for owners of Left 4 Dead 2, the zombie shooter sequel. Word is the DLC "features 3 new maps, new weekly game modes (Mutations), a new 'uncommon common' zombie class (the fallen survivor), melee weapon (golf club), firearm (M-60), support for infected bot play in Versus, 10 new achievements and more!" To celebrate the release, Left 4 Dead 2 is on sale for 33% off through Monday.